Displays are being designed to meet high-resolution needs of consumers displaying video content from various video applications, such as digital video disk (DVD) players, multimedia video, and video games. However, not all video applications are desired to run at the maximum resolution provided by the display. For example, a consumer may prefer to set a display resolution associated with his operating system to a lower resolution than a display's maximum resolution. The lower resolution may be desired due to the increase in size of text being displayed, making it easier for consumers with poor eyesight to read the text.
Problems arise when attempting to set certain displays to display images at a lower resolution than the displays are designed for. In multisync cathode ray tube (CRT) displays, the change in image resolution setting is not problematic. Multisync CRT displays may be set to display video with a lower display resolution by altering the scanning rate of the CRT display. By decreasing the scan rate of the CRT display, lower resolution video may be supported. Pixelated displays, such as flat panel, liquid crystal displays, or digital light projectors, are fixed resolution displays. It is sometimes difficult to alter the resolution of pixelated displays. Unlike multisync CRTs, pixelated displays are fixed-format, in that an identifiable, or unique screen pixel is provided for every image pixel displayed on the display. When an image is to be presented at a lower display resolution than directly supported by a resolution the pixelated display, the image may need to be scaled up to match the resolution of the pixelated display.
Some attempts have been made to remedy the problem associated with altering the scaling of images for pixelated displays. One solution is to not rescale the display image, and leave the one-to-one relationship between image pixels and display pixels intact. Unfortunately, the result is that the image is only displayed on a portion of the display screen. The image is generally centered in the screen and small, making the effect of setting the video to a lower resolution somewhat negligible. Generally, ratiometric expansion is performed, in which attempts are made to scale the image to match the display resolution, for example by replication.
Replication is a method of replicating pixels of a source image to increase the resolution of the source image. Unfortunately, not all replicated portions of an image are proportionately increased in size. Replication works fine with some upscale factors, such as one to two where every pixel is simply replicated to two pixels. However, when the upscale factor is not an integer multiple, it is not always certain how many pixels to replicate from a single pixel. While a pixel may be replicated to a first number of pixels in one portion of the display, the pixel is replicated to a different number of pixels in another portion of the display. This artifact is especially noticeable in text and may generate unfavorable results.
Another method of scaling an image is to re-sample the image. As shown in prior art FIG. 1, a new image, closer to a preferred resolution of the display, is re-sampled from the source image. Pixels P1–P3 of a source video line 110 are re-sampled into pixels R1–R5 of a re-sampled video line 120. In the illustrated embodiment, a scale factor of 2.5× is used to generate re-sampled video line 120. Distances between pixels of the source video line 110 and corresponding pixels in the re-sampled video line 120 are measured in steps of 0.4 pixels. The distances are used to generate absolute alpha values 112. Absolute alpha values 112 may be used to generate interpolated pixels R1–R5. Source video line 110 represents a particular line of pixel values corresponding to a source video image. In one embodiment, the source video image corresponds to video generated by an information handling system for display on a pixelated display (not shown). The resolution of source video line 110 is lower than a desired resolution on a pixelated display. To get the desired image resolution, source video line 110 is re-sampled to a re-sampled video line 120, which represents source video line 110 with a 2.5 scale factor.
Each of the pixels (R1–R5) of re-sampled video line 120 may be associated with a position relative to pixels in source video line 110. The relative positions are represented through absolute alpha values 112. In the illustrated embodiment, the absolute alpha values denote a distance from the nearest left pixel in source video line 110. Pixel R1 of re-sampled video line 120 is mapped part way between pixel P1 and pixel P2; accordingly, the absolute alpha value associated with pixel R1 is 0.5. Pixel R2 is mapped close to pixel P2 but far from pixel, P1. R2 is assigned an alpha value of 0.9. Step increases between absolute alpha values assigned for a next right pixel of re-sampled video line 120 is inversely proportional with an assigned scale to be performed. For example, with a scale of 2.5×, a step in alpha value for every next pixel of re-sampled video line 120 is 1/2.5, or 0.4. Therefore, the absolute alpha value assigned to pixel R3 is 1.3; however, the ‘1’ may be dropped to indicate pixel R3's relative distance to the nearest left pixel, P2. Therefore, the absolute alpha value associated with pixel R3 is 0.3. The absolute alpha value associated with pixel R3 is 0.7. The absolute alpha value associated with pixel R5 is taken from pixel P3, and is 0.1. The next pixel of re-sampled video line 120, pixel R6 (not shown) would be taken from pixel P3 and would be 0.5, indicating that pixel R6 may be mapped between pixels P3 and R4.
The absolute alpha values 112, indicate the relative positions of pixels R1–R5 of re-sampled video line 120 to pixels P1–P3 of source video line 110. The absolute alpha values may be used to determine the values of pixels R1–R5. Coefficients based on the absolute alpha values may be used as weights to combine the values of the relatively nearest left and right pixels. In one embodiment, taking a difference of 1 and an assigned absolute alpha value generates the coefficients. For each pixel of re-sampled video line 120, the value of the nearest left pixel of source video line 110, multiplied by the difference of 1 and the assigned alpha value, is added to the value of the nearest right pixel, multiplied by the assigned alpha value. Using the values of P1–P3 and the assigned alpha values of absolute alpha values 112, the following equations may be used to determine values for pixels R1–R5:
R1=P1(1−0.5)+P2(0.5)=P1;
R2=P1(1−0.9)+P2(0.9);
R3=P2(1−0.3)+P3(0.3);
R4=P2(1−0.7)+P3(0.7); and,
R5=P3(1−0.1)+P4(0.1).
Such methods of re-sampling, such as through a two-tap, bilinear re-sampler as in prior art FIG. 1, allow a lower resolution image to be up-scaled to a desired display resolution. Unfortunately, the re-sampled results may appear blurry. As rates of change associated with portions of the image being displayed reach the Nyquist rate of the image's resolution, the re-sampled representations of the portions are blurred. The Nyquist rate of the image's resolution is half of the total resolution of the image, indicating the highest possible frequency to be displayed at the resolution of the image. While most “real world” video, such as digital video disk (DVD) video, is band limited well below the Nyquist rate of the image's resolution, text is generally not. Specifically, letters such as ‘w’ provide rapid rates of change which become blurred and difficult to read in re-sampled images. From the above discussion, it is apparent that an improved system for scaling images for display is needed.